In general, when evaluating the change in physical ability and exercise ability of an aging person, there is a means to estimate about what age such person's ability corresponds to, by comparing with the average known ability corresponding to a certain age.
It is known that hairs become thinner, decrease in number, become gray, and become dry with age (Non-Patent Document 1). Techniques that have been proposed for evaluating hair properties include measuring and analyzing the physical properties of hair strands such as tensile strength and extension rate (Patent Document 1), and making a comprehensive evaluation of microscopic images of hair strands, taking measurements such as gloss and hue, evaluating scores of various questionnaires, and so on (Patent Document 2). There has been no simple technique, however, for evaluating the equivalent age of hair objectively.
[Non-Patent Document 1] C. R. Robbins, “Chemical and Physical Behavior of Human Hair,” pp. 77-79, Springer-Verlag, New York, 2002
[Patent Document 1] JP-A-7-306200
[Patent Document 2] JP-A-2000-287953